Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$31.26	6.125%	$33.1747	$33.17	$33.15	$33.20
Purchase #2	$74.38	5.448%	$78.4322	$78.43	$78.45	$78.40
Purchase #3	$113.42	5.125%	$119.2328	$119.23	$119.25	$119.20
Purchase #4	$52.28	8.104%	$56.5168	$56.52	$56.50	$56.50
Purchase #5	$106.76	6.735%	$113.9503	$113.95	$113.95	$114.00
Purchase #6	$79.75	3.198%	$82.3004	$82.30	$82.30	$82.30
Purchase #7	$100.71	13.344%	$114.1487	$114.15	$114.15	$114.10
7 purchase totals =	$558.56		$597.7559	$597.75	$597.75	$597.70